The present invention relates to a method for stabilizing a car-trailer combination consisting of a towing vehicle and a trailer or semi-trailer. The invention further relates to a driving dynamics control system for stabilizing a car-trailer combination consisting of a towing vehicle and a trailer or semi-trailer, which is appropriate for implementing the method.
Car-trailer combinations, which consist of a towing vehicle and a trailer or semi-trailer, exhibit an unstable driving performance starting from a defined limit speed. Above the limit speed, swaying motions of the trailer or semi-trailer occur, with their amplitudes rising. Especially when driving on the highway car-trailer combinations frequently reach the limit speed so that swaying motions of the trailer are provoked which partly cause serious accidents. The reason is that operators of average skills are generally unable to stabilize a swaying car-trailer combination to a sufficient degree because steering movements which are performed for stabilization, due to the response time, are not in the necessary phase relation to the swaying motions so that these are even amplified under certain circumstances.
To stabilize car-trailer combinations, driving dynamics control systems are known in the art which detect yaw oscillations of the car-trailer combination in a robust fashion and stabilize the car-trailer combinations by braking interventions independently of the driver. As this occurs, the speed of the car-trailer combination is reduced below the limit speed. It is furthermore known to use automatic steering interventions, in which a steering angle at the steerable wheels of the towing vehicle is set independently of the driver by way of a steering actuator, or braking interventions in order to produce a yaw torque which dampens the yaw oscillations. The yaw torque is determined in particular from a deviation between a detected actual yaw rate and a reference yaw rate, which usually is calculated using a vehicle model especially based on a steering angle signal that is representative of the direction requested by the driver.
However, the problem is encountered in this respect that the steering angle signal which is included in the calculation of the reference yaw rate can exhibit signal oscillations which are due to the swaying motions of the trailer. The signal oscillations can be provoked especially by steering movements, which are performed by the driver or the steering actuator for compensation of yaw oscillations of the car-trailer combination. This can impair the driving dynamics control and, more particularly, cause erroneous interventions of the control system.